The building housing Libyan state oil energy firm the National Oil Corporation (NOC) is seen in Tripoli, February 22, 2016. Reuters / Ismail Zitouny

BENGHAZI, Libya: A parallel national oil corporation allied to Libya’s eastern government was loading a shipment of 650,000 barrels at the Marsa el-Hariga terminal on Monday in an effort to sell oil for the first time, officials said.

The eastern NOC has long been trying to sell oil, but has been opposed by the Western-backed NOC in Tripoli, which says any such sale would be in breach of U.N. Security Council resolutions.

The eastern NOC has said that efforts to load the Indian-flagged Distya Ameya at the end of last week were foiled by pressure from the NOC in Tripoli.

Loading of the tanker started on Monday morning and would be finished later in the day, an official with the eastern NOC in Benghazi said. Eastern NOC head Nagi al-Maghrabi confirmed by text message that the tanker was loading, and a Hariga port official said the tanker was expected to sail later on Monday.

A spokesman for the NOC in Tripoli, Mohamed al-Harari, said there were two tankers docked at Hariga terminal competing to load the shipment for the rival NOC branches.

He said that if the Distya Ameya managed to load the shipment and leave the port, he hoped the international community would act to block it.

In 2014, a group pressing for more autonomy in eastern Libya shipped crude from Es Sider terminal, but U.S. special forces boarded it off Cyprus and forced it to return.

The NOC in Benghazi claims legitimacy through the eastern government, which was nominated by Libya’s internationally recognised parliament.

That government and parliament moved to the east as armed groups that took control of Tripoli in 2014 installed a rival set of institutions in the capital.

Last month a U.N.-backed unity government arrived in Tripoli, where it is gradually trying to establish its authority. The NOC in Tripoli has said it will work with the new government to coordinate future oil sales.

Last month the U.N. Security Council said the unity government had “primary responsibility” for preventing illicit oil sales, urging it to communicate any such attempts to the U.N. committee overseeing Libya-related sanctions.

The resolution also restated a call for member states to cease contact with any “parallel institutions”.

Libya’s output has fallen to less than a quarter of the 1.6 million barrels per day produced before the 2011 uprising that toppled autocrat Muammar Gaddafi.

(Reporting by Aidan Lewis in Tunis and Ahmad Gaddar in London. Writing by Aidan Lewis; Editing by Richard Balmforth)